1. Field of the Invention
The present invention relates generally to an apparatus and a method for manufacturing a polymer dispersion type liquid crystal display (LCD) device, and more particularly to an apparatus and a method for manufacturing a polymer dispersion type LCD device having a polymer dispersion liquid crystal (LC) layer (a composite layer of LC and high polymer resin) with a uniform internal structure.
In addition, this invention relates to an apparatus and a method for manufacturing a plurality of polymer dispersion type LCD devices having uniform characteristics.
2. Description of the Related Art
A polymer dispersion type LCD device usually comprises a liquid crystal (LC) cell formed by coupling a pair of transparent substrates having transparent electrodes with a frame-shaped sealing member interposed there between; and a polymer dispersion LC layer situated within the LC cell. The polymer dispersion LC layer comprises a composite layer of resin and LC. In general, a nematic liquid crystal having a positive dielectric anisotropy is used as LC.
LC molecules in the polymer dispersion LC layer are orientated in various directions when no voltage (electric field) is applied between mutually opposed electrodes. In this state, light incident on the polymer dispersion LC layer is scattered by a light scattering function of the-polymer dispersion LC layer and, in the case of a transmission type LC element, the display is set in a dark (black) mode. When a predetermined threshold voltage or a higher voltage is applied between the mutually opposed electrodes, LC molecules are uniformly orientated in a vertical direction to the surfaces of the substrates. In this state, the light incident on the polymer dispersion LC layer is hardly affected by the light scattering function and passes through the polymer dispersion LC layer. In the case of the transmission type LC element, the display is set in a light (white) mode. As has been described, the polymer dispersion LCD device displays a desired pattern such as a character or a figure by means of transmission and scattering of light.
In general, the polymer dispersion LCD device is manufactured by the following steps. An LC cell is formed by coupling a pair of transparent substrates with a frame-shaped sealing member interposed. By means of a vacuum injection method, a mixture solution of a polymer material (monomer, oligomer, etc.), which can be subjected to a polymerization reaction by light, and a liquid crystal is filled in the LC cell.
The LC cell filled with the mixture solution is mounted on a cell support, and the LC cell is irradiated with light from above. Thus, the double bond of the polymer material, which is in the state of a monomer or an oligomer, is released, and the polymer material is separated into radicals. The polymer material is polymerized by a radial polymerization reaction in which adjacent high-molecular radicals are bonded to one another. Thus, a polymer dispersion LC layer in which LC is dispersed in a polymer resin layer is formed.
In the above manufacturing method, light is radiated on the upper surface of the LC cell to subject the polymer material in the mixture solution to light polymerization. Consequently, a polymer dispersion type LCD device having good characteristics cannot be obtained. More specifically, if light is radiated on one surface of the LC cell, the intensity of light for light-polymerizing the polymer material differs between the light radiation side (upper side) and the opposite side and the rate of light polymerization differs. As a result, the internal structure of the formed polymer dispersion LC layer, i.e. the LC dispersion state, differs between one side and the other side of the LC cell, and the electro-optical characteristics of the LCD device are degraded.
Moreover, if the polymer material is irradiated with light at the time of storage, polymerization progresses partially. To prevent this, the polymer material needs to be stored in the state in which it is perfectly shielded from light. It is difficult, however, to store the polymer material in the state in which it is perfectly shielded from light. Besides, when the polymer material and liquid crystal (LC) are mixed, or when the mixture solution is injected in the LC cell, polymerization of the polymer material may progress partially due to light leakage.
This being the case, when a polymer dispersion LC layer is formed, a variation occurs generally in characteristics of the polymer material due to a time-basis variation (a variation of molecular amount due to progress of polymerization), etc. Even if a predetermined amount of ultraviolet is radiated on the mixture solution in this state to form the polymer dispersion LC layer, the characteristics of the formed polymer dispersion LC layers differ from element to element or from lot to lot, a variance occurs in the degree of scattering of light, and the uniformity of the display characteristics of LCD devices is lost.